Electrical cables, such as shielded cables, and associated connectors frequently are used in military applications and other industrial cable assembly applications. In such applications, the connector/cable interface often is environmentally sealed and should provide a superior strain relief connection to ensure that the quality of the electrical connection is not affected by any physical abuse to which the connector and cable might be subjected.
Typically, an industrial-type connector found in such a cable assembly is provided with a backshell and a front connector combination which are mechanically connected to one another. The backshell mechanically supports and secures the cable for strain relief. The backshell often may be provided with a plurality of components for achieving shielding, sealing and/or strain relief. In practice, there have been various types of strain relief structures in the connector or backshell assemblies, three types being most prevalent. The first and most common type of strain relief is to provide a conventional split shell screw-type clamp which is positioned over the connector and backshell after assembly and then tightened by one or more screws to effect a gripping strain relief about the cable. This type of strain relief structure does not provide uniform stress throughout the clamp, and uneven wear and ultimate insulation breakage eventually may be caused at the stress points.
A second type of strain relief structure is embodied in a grommet compression-type backshell which includes a rubber or other elastomeric grommet or sleeve which is compressed onto the cable to provide strain relief therefor. The grommet usually is provided primarily as a seal for the connector, and the strain relief function is secondary and, consequently, usually inadequate. In addition, elastomeric rings do not provide uniform clamping pressure throughout the entire circumference thereof when subjected to considerable radial compressing forces.
A third type of strain relief structure is shown in U.S. Pat. No. Re. 33,611 (and corresponding parent U.S. Pat. No. 4,857,015) to Michaels et al, dated Jun. 11, 1991 and assigned to the assignee of this invention. As disclosed therein, a coiled strain relief spring is formed in a generally toroidal configuration which is dimensioned to receive an insulated cable axially therethrough. The coil spring is radially compressible to achieve a secure strain relief engagement with a jacketed cable on compression by a compression nut of the backshell assembly. This system uses few components and has been shown to give superior performance in strain relieving a cable due to the fact that the spring radially compresses as it is biased by a frustoconical camming surface, resulting in no high points of compression or stress. Still, in some applications, it has been found that the spring will rotate with the compression nut as the nut is rotatably coupled to the backshell. Rotation of the strain relief coil spring can cause wear and damage to the jacketed cable and possibly cause breakage of the individual conductors of the cable. The present invention is directed to still a further improvement wherein means are provided to prevent rotation of the strain relief coil spring when it is compressed onto the cable by relative rotation between two connector members, such as the backshell and the compression nut.